Lasers have long been known in the art for a wide variety of uses. These sources of light are arranged to function at a certain predetermined wavelength. In some applications, it is unimportant whether the wavelength of the laser remains essentially constant over time. However, in other applications, such as optical telecommunications, and medical lasers, it is crucial that the preset wavelength be maintained throughout the use of the laser. This is necessary due to aging of the laser, as well as the in environmental effect of temperature, two of the major factors affecting laser wavelength.
A number of proposals have been made in the literature as to ways to monitor and control lasers. In particular, much research has been conducted in the area of telecommunications over optical fiber lines. The most common solution is to use an outside wavelength reference from, for example, a synchronized Etalon filter which provides a set of equally spaced references at the standardized wavelengths, or from a frequency stabilized master laser. However, these devices require additional expensive equipment as well as temperature control and stabilization of the Etalon or master laser. Thus, these devices rely on an external reference source to maintain the laser wavelength.
Another solution is to use a reference filter. Yet another suggestion is to lock the wavelength comb of a tunable DBR to a waveguide grating router to enable a laser to track and correct uncontrolled changes in a remotely located WDM device. Another is to use an arrrayed-waveguide grating. Yet another utilizes a narrow-band reflective fiber grating at a temperature sensor at the remote receiver. A further proposal includes a frequency control scheme where the frequency of each transmitter is referenced to a silica based optical frequency discriminator, which in addition is locked to an absolute reference frequency. It has also been suggested to use cascaded fibre Bragg gratings as channel allocators for unequally spaced channel multiplexing, and multiwavelength lasers can be successfully locked to the transmission dips produced from the cascade FBG's by using the dithering technique. These proposed devices are generally complicated mechanically and expensive, requiring a number of filters arranged with high accuracy.
Accordingly, there is a long felt need for a simple device for monitoring and controlling laser wavelength which is relatively simple to build and maintain, highly accurate, and which is substantially unaffected by temperature, and it would be very desirable to have such a device which does not rely on an external reference wavelength,